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New Standards Impact Card-Edge Connector Design

Next-generation DDR4 DIMM and PCIe specifications are having the biggest impact on card-edge connector designs used in computers, workstations, servers, routers, switches and other networking equipment. A big part of these standards are related to speed.

"Higher speed requirements are one of the things changing the design and performance of the card-edge connector," said Bill Kysiak, regional product manager for Molex Inc., based in Lisle, Ill.

This impacts the level of engineering required to design and manufacture the part and drives the need for additional signal integrity (SI) data.

DIMM and PCIe connectors are looking more like high-speed devices, so these products require more signal integrity information, according to Kysiak. "We are challenged with providing signal integrity data and the higher technology to ensure that the products perform at the speeds required by the computers."

Like all interconnects, card-edge connectors are challenged by the need for increased data rates. "This challenge requires connector companies like TE Connectivity to evaluate and rethink the receptacle contact structure and work closely with the PCB manufacturing industry to understand their process capabilities," said a TE Connectivity spokesperson. "We need to be able to design a product with the next level of speed, while maintaining its backwards compatibility, which is a key request of end markets."

TE reported its Mini SAS High Density (HD) connector is an example of how a card-edge connector has been impacted by both miniaturization and the need for higher data rates. "Almost all requirements are driven by industry standard groups who reflect the markets' needs."

Green issues impact design

"Materials pricing has been relatively stable, and in some cases, has backed off a little bit from its peak," said Dave Sideck, FCI USA's global strategic marketing manager.
Environmental issues also play a role in the design of card-edge connectors. There are new requirements for RoHS-compliant, lead-free compatible materials.

"The lead-free requirement, which is a plating change, also impacts the plastics," Kysiak said. "The lead-free contact has to go through a surface-mount line at a higher temperature in order to solder properly, which requires the housing to be constructed of a different material that can withstand the higher processing temperature."

There is also a call for halogen-free connectors, particularly from larger OEMs. "It requires new materials, but it adds a slight cost to the connector," noted Kysiak.

"One of the challenges next year will be the preparation for DDR4 memory sockets, which are card-edge connectors," according to David Sideck, global strategic marketing manager for FCI USA LLC, in Etters, Pa. He said the migration from DDR2 to DDR3 was “relatively painless because the contact structure wasn't very different. They were still connectors on 1.00 mm pitch.”

With the move to DDR4, which will happen in early 2014 when Intel rolls out its new processors, DDR4 sockets will be entirely new connectors.

DDR4 will require a finer pitch connector to meet the need for increased packaging density. The original DIMM connector started at a 1.27 mm pitch then moved to a 1.00 mm pitch.

"Now we're in the process of moving to a .85 mm pitch on the new DDR4,” said Kysiak. "Every time we go to a finer pitch, the whole process is a little more difficult.”

Sideck noted that the move to 0.85 mm pitch requires a new contact structure and new housings. "We'll have to tool the products up to support mass production and go through connector qualification processes at the OEMs," he said.

FCI reported that server manufacturers are looking for DDR4 connector samples ahead of Intel's new server processor introduction in early 2014. FCI is sampling vertical, surface-mount DDR4 DIMM sockets now.

In addition, PIC-SIG is in the final stages of wrapping up the PCIe Gen 3 performance specifications, which increases the data transfer rate of the connectors from 5 to 8 Gbits/s.

However, Sideck said connector manufacturers did not have to do much to support the new generation, with the exception of additional verification testing. "Many existing products already meet those requirements," he said.

New challenge

The next challenge for the card-edge connector market is making the transition from 8 to 16 Gbits/s, which will require some new product development, according to Sideck. The industry workgroup is beginning to address that within PCI-SIG.

"One challenge is that it needs to remain backwards compatible," said Sideck. "It will need to accept previous generation PCIe add-in cards, which puts constraints on what can be changed within the system. You can't change the interface or slot dimensions very much because they still need to work with older generation cards."

The server industry is also adopting power card-edge connectors for new generation servers. Sideck reported that FCI's HPCE (high power card edge) offers three key advantages for power supply applications including higher current contact rating, a thin profile, and housing features to enhance heat dissipation.

Another benefit is that the HPCE connectors are available with power and signal contacts integrated into a single molded housing. Users can define the number of contacts and where they want to place the power and signal contacts, according to Sideck.

Supply should not be an issue. FCI recently announced 3M as a second source for the HPCE connectors.

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